GE D90 Plus Instruction Manual page 163

CHAPTER 6: COMMUNICATIONS
Using direct inputs and outputs for pilot-aides schemes
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
Figure 132: Direct input and output settings for IED 4
Message delivery time is approximately 0.2 of power system cycle (at 128 kbps) multiplied
by the number of bridges between the origin and destination. Dual-ring configuration
effectively reduces the maximum communications distance by a factor of two.
In this configuration the following delivery times are expected (at 128 kbps) if both rings
are healthy:
Table 9: Delivery times for healthy rings
Path
IED 1 to IED 2
IED 1 to IED 3
IED 1 to IED 4
IED 2 to IED 3
IED 2 to IED 4
IED 3 to IED 4
If one ring is broken (say TX2-RX2), then the delivery times are as follows:
Table 10: Delivery times for rings with break in TX2-RX2
Path
IED 1 to IED 2
IED 1 to IED 3
IED 1 to IED 4
IED 2 to IED 3
IED 2 to IED 4
IED 3 to IED 4
A coordinating timer for this bus protection scheme could be selected to cover the worst
case scenario (0.4 of a power system cycle). Upon detecting a broken ring, the coordination
time should be adaptively increased to 0.6 of a power system cycle. The complete
application requires addressing a number of issues, such as failure of both the
communications rings, failure, or out-of-service conditions of one of the IEDs. Self-
monitoring flags of the direct inputs and outputs feature would be primarily used to
address these concerns.
Consider the three-terminal line protection application shown below.
DIRECT INPUTS AND OUTPUTS
Delivery time
0.2 of a power system cycle
0.4 of a power system cycle
0.2 of a power system cycle
0.2 of a power system cycle
0.4 of a power system cycle
0.2 of a power system cycle
Delivery time
0.2 of a power system cycle
0.4 of a power system cycle
0.6 of a power system cycle
0.2 of a power system cycle
0.4 of a power system cycle
0.6 of a power system cycle
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